Heat-resistant and corrosion-resistant high chromium-nickel alloy

ABSTRACT

A heat-resistant and corrosion-resistant high chromium-nickel alloy, consisting of 32 to 40 percent by weight chromium, 2 to 9 percent by weight tantalum, 2 to 5 percent by weight molybdenum, 0.5 to 3 percent by weight (aluminum + titanium), 0.05 to 0.5 percent by weight carbon, 0.025 to 0.35 percent by weight boron, with the remainder being substantially nickel and incidental impurities is provided. This alloy is not only characterized by excellent heat-resistant properties and excellent corrosion-resistance, but is also characterized by very great mechanical strength properties at elevated temperatures, and has good high temperature workability so that it can be formed by hot forging techniques. Hence, this alloy is suitable for the construction of parts which require great mechanical strength properties at elevated temperatures, such as gas turbine blades which operate under low grade residual fuel oil combustion.

United States Patent [191 Shimotori et al.

[ June 11, 1974 HEAT-RESISTANT AND CORROSION-RESISTANT HIGHCHROMlUM-NICKEL ALLOY Inventors: Kazumi Shimotori; Hirokazu Tokoro, bothof Kawasaki; Shinichi Nakamura; Katsuhiko Kawakita, both of Yokohama,all of Japan Tokyo Shibaura Electric Co., Ltd., Kawasaki-Shi, JapanFiled: Apr. 10, 1972 Appl. No.: 242,799

Assignee:

Foreign Application Priority Data Apr. 15, 1971 Japan 46-23479 US. Cl.75/171, 75/134 F, 148/325 Int. Cl. C22c 19/00 Field of Search 75/171,170, 134 F;

References Cited UNITED STATES PATENTS 10/1951 Bieber et a1. 75/17110/1957 Bloom et al. 1/1962 Grant et a1 75/171 Primary Examiner-Richard0. Dean Attorney, Agent, or'Firm-Oblon, Fisher. Spivak. McClelland &Maier [5 7] ABSTRACT A heat-resistant and corrosion-resistant highchromium-nickel alloy, consisting of 32 to 40 percent by weightchromium, 2 to 9 percent by weight tantalum, 2 to 5 percent by weightmolybdenum, 0.5 to 3 percent by weight (aluminum titanium), 0.05 to 0.5percent by weight carbon, 0.025 to 0.35 percent by weight boron, withthe remainder being substantially nickel and incidental impurities isprovided.

1 Claim, No Drawings HEAT-RESISTANT AND CORROSION-RESISTANT HIGHCHROMIUM-NICKEL ALLOY BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a heat-resistant andcorrosion-resistant high chromium-nickel alloy.

2. Description of the Prior Art Heretofore, industry has relied onnickel base super alloys, such as those strengthened by y (Gammaprime)-Ni (Al, Ti) phase, and cobalt base super alloys, for applicationsrequiring good heat-resistant properties.

An increasing demand has been developing, however, for alloy materialswhich not only have excellent high temperature mechanical properties,but which also possesses excellent corrosion resistance at elevatedtemperatures. Such an alloy would find wide application in the chemicalprocessing industry and as structural material in the construction ofthermal engines.

' Heretofore, attempts were made to improve the antioxidative propertiesof conventional super alloys by the incorporation of increased amountsof chromium. The chromium conent, content, is limited by the fact thatadded quantities of chromium to conventional alloys will adverselyaffect the high temperature mechanical properties.

In general, the maximum amount of chromium contained in the alloy wasabout 28 percent by weight, and usually no more than 20 percent byweight. While these additional quantities of chromium did have somebeneficial effect in enhancing anti-oxidative properties, it was at besta compromise between enhanced antioxidative properties and reduced hightemperature mechanical strength.

A need exists, therefore, for a high chromium-nickel alloy which ischaracterized by excellent heat resistance, excellent corrosionresistance and strong mechanical strength at elevated temperature.

SUMMARY OF THE INVENTION Accordingly, it is one object of this inventionto provide a high chromium-nickel alloy, which possesses excellentheat-resistance, excellent corrosion-resistance and good hightemperature mechanical strength properties, and has good hightemperature workability, so that it can be hot forged.

Another object of this invention is to provide a structural materialwhich is satisfactory for application in the construction of parts whichwill be subjected to high temperature and high stress service, such asgas turbine blades for turbines using low grade residual fuel oils.

These and other objects have now herein been attained by providing ahigh chromium-nickel alloy consisting of 32 to 40 percent by weight ofchromium, 2 to 9 percent by weight tantalum, 2 to percent by weightmolybdenum, 0.5 to 3 percent by weight (aluminum titanium), 0.05 to 0.5percent by weight carbon, 0.025 to 0.35 percent by weight boron, withthe remainder being substantially nickel and incidental impurities. In

- one embodiment, the alloy of this invention may be a mixture ofmanganese, silicon, calcium, magnesium, rare earth elements andscavenger such as MISCI'I metal.

DETAILED DESCRIPTION OF THE INVENTION The effect of each elementcontained in the alloy of this invention is as follows.

Chromium, (aluminum titanium) and boron provide good high temperaturecorrosion-resistance. If the chromium content exceeds the upper limit of40 percent, an a phase may appear in large quantities in solidificationof the alloy. If the chromium content is less than 32 weight percent,satisfactory corrosionresistance will not be obtained. Chromium,tantalum, molybdenum and (aluminum titanium) improve the hightemperature mechanical strength. In particular, tantalum has anoutstanding ef fect on the high temperature mechanical strength.

The use of tantalum enables significant increases in high temperaturemechanical strength while the use of chromium enables goodcorrosion-resistance. If the alloy contains greater than 9 weight percent tantalum, there will be little increase in high temperaturemechanical strength.

The addition of 5 weight per cent molybdenum can render the alloybrittle because of the formation of a Sigma (0') phase over long periodsof heating. Also, it renders the alloy more corrosive to hightemperature oxidation.

(Aluminum titanium) are the most effective additions to improvemechanical strength. The effectiveness of each of aluminum and titaniumon the mechanical strength and corrosion-resistance is nearly equal.However, if amounts of greater than 3 weight percent are used, the alloycan become brittle and the long time stress rupture strength willdiminish due to the appearance of an a phase.

Carbon will decrease hardness of the alloy and increase elongation andis essential for long time stability of creep strength. More than 0.5weight percent carbon, however, is undesirable because it will reducethe corrosion resistance of the alloy.

Comparatively, the boron content of the alloy of this invention isgreater than used in conventional alloys. If the boron content falls tobelow 0.025 weight percent, however, its effectiveness is reduced. Onthe contrary, if the boron content exceeds 0.35 weight percent, thealloy will become brittle.

The alloy of this invention, therefore, is characterized by excellenthigh temperature corrosion-resistance and excellent high temperaturemechanical strength.

At high temperatures, the alloy of the invention will form a Gamma (7)phase matrix. Accordingly, it is desirable to heat treat the alloy tostabilize the structure, at a temperature adjacent to the usetemperature to form the Gamma (-y) phase.

Having now generally described the invention, a further understandingcan be obtained by reference to certain specific examples which areprovided herein for purposes of illustration only and are not intendedto be limiting unless otherwise specified.

EXAMPLE 1 mold to form the shape of a rod. After solution-treating Ti),C and B provided remarkable increases in the 10 high temperaturemechanical strength.

TABLE T ple was weighed into an alumina crucible and was melted by highfrequency heating. The molten mass of alloy obtained was cast into ametal mold to form the shape of a rod. After solution-treating at atemperature of 1,220C. for 4 hours in order to form the f.c.c. Gamma (7single phase structure, the rod was permitted to cool in air. The testpieces were cut from the sound portion of the bar (or rod) by X-rayanalysis, and were aged to stabilize the structure, at a temperature ofCompositions of Samples Sam 1:: Composition bv we igl t) No r AI Mo Ta CB Ni A- I 31 36 0.5 1 4 5 0.2 0.2 Balance A-76 32 l 1 4 5 0.2 0.2 do.A-77 40 I 1 4 5 0.2 0.2 do. A-36 36 l 1 4 2 0.2 0.2 do. A-72 36 l l 4 80.2 0.2 do. 8-75 36 1 l 5 0.2 0.2 do. A-32 36 I 1 5 5 0.2 0.2 do. B-7336 0 0 4 5 0.2 0.2 do. A-127 36 0 0.5 4 5 0.2 0.2 do. A-135 36 1.5 1.5 45 0.2 0.2 do. B-39 36 1 l 4 5 0 0 d0. A-78 36 l l 4 5 0.05 0.2 do. A-7936 l 1 4 5 0.5 0.2 do. A-92 36 1 1 4 5 0.2 0.025 do. A-54 36 1 l 4 5 0.20.35 do. 8-90 36 1 1 4 5 0.2 0.5 do. 8-38 36 1 l 4 1 0 0 do.

TABLE 11 Results of Tests 800C. kg/mm creep Tensile test at 800C. in thepull Sample rot velocity of mmlmin.

No. Rupture time Elongation Tensile strength Elongation (hr.) (kg/ A-13185.0 10.7 68.0 10.0 A-76 32.7 4.8 66.2 8.2 A-77 72.6 1.9 70.9 4.1 A-3634.5 2.6 65.3 13.4

8-75 20.5 3.6 58.0 0 A-32 82.4 3.8 76.4 1.2 B-73 5.4 23.1 24.7 32.1 A42730.5 21.2 48.1 12.7 A-135 46.3 5.7 89.1 2.2 8-39 65.0 0 71.3 3.5 A7864.1 4.3 68.1 8.1 A-79 78.3 9.2 60.1 5.0 A-92 62.1 4.5 56.0 11.0 A-5461.3 3.6 60.3 2.6 8-90 18.3 0 69.3 3.0 8-38 14.9 2.3 57.6 4.3

3 Moreover, it was found that the additions of C and" B providedremarkable increases in the character of long time creep strength.

TABLE 111 Results of Creep Tests Sample Rupture time (hr.)

No. 800C. 15 kg/mm creep EXAMPLE 2 In this example, the effects of someelements on cor- 5 temperature of 1,100C. The corrosive weight lossafter heating for 30 hours is shown in Table IV. As shown in that Table,the sample of this invention showed greater corrosion resistance thanU-500 (a conventional Ni base alloy). The relation between the amount ofadditional elements and the corrosive weight loss of alloy is shownindustrially by the empirical formula: AW=155 3.0 Cr% +5.0 (A1% Ti%) 1.5Co% 758% 25.5C% 1.6 (Mo% /W%) 0.5 Ta% 4.0 Nb% at 1,100C.

Where AW (mg/cm /hr.) is the corrosive weight loss per unit surface areaper unit hour at l,l00C.

Chromium imparts corrosion-resistance to these alloys of this invention,and saves mg/cm of corrosive weight loss per unit weight percent. Also,(aluminum .titanium) and boron effectively improve thecorrosionresistance.

900C. for 2 hours. Thereafter, the test pieces were subjected to acorrosion test with a synthetic ash at a TABLE IV Results of corrosiontest with a synthetic ash* synthetic ash (207! by weight Na,SO,+ 80% byweight V Where S-8 1 6 (control): 0.38 weight C, 20 weight Cr, 20 weightNi, 4 weight Mo, 4 weight W, 4 weight Nb, 4 weight Fe, remainder Co.

U-500 (control): 0.08 weight C, 18 weight Cr, 19 weight Co, 4 weight M0,2.9 weight Al, 0.006 weight B, 0.05 weight Zr, remainder Ni.

From the results as above mentioned, it was found that Ta, Mo, (Al Ti),C and B were substantially effective in achieving a high Cr-Ni alloyhaving the desired properties as enumerated in the objects.

In general, Nb can be substituted for Ta, Zr can be substituted for Band W can be substituted for Mo. These substitutions, however, are notas effective as the preferred components. Namely, Nb and Zr aresignifimay inferior to Ta or B in corrosion-resistance. Moreover, theeffect of W on the tendency to promote Sigma (rr) phase is differentfrom that of Mo. Nevertheless. if desired. up t o 10 to 20 percent byweight of the Ta, B or Mo may be substituted by the elements Nb, Zr andW as above mentioned, and the similar characteristics will still beobtained. Cobalt, in amounts of less than a few percent, may be substituted for nickel.

It is necessary to avoid the addition of iron (Fe) to the alloy. If morethan 2 to 3 percent by weight iron (Fe) is added to the alloy, the alloywill be severely hardened and will be more brittle in mechanicalpropert1es.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of theinvention. Accordingly,

What is claimed as new and intended to be covered by letters patent is:

l. A heat-resistant and corrosion-resistant high chromium-nickel alloyconsisting essentially of 36 to 40 percent by weight chromium, 5 to 9percent by weight tantalum, 2 to 5 percent by weight molybdenum, 0.5 to3 percent by weight (aluminum titanium), 0.05 to 0.5

percent by weight carbon, 0.025 to 0.35 percent by weight boron, and theremainder beingsubstantially nickel and incidental impurities.

